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1.Introduction (1/2)<br />There are several spectrum issues related with remote sensing. Some issues have been resolved thorough WRC, study groups SG7, Working Party of WP7C of ITU-R in collaboration with various space agencies and remote sensing community such as GRSS FARS (Frequency allocation for Remote Sensing). <br />These issues cover not only spaceborne active sensor such as cloud radar, precipitation radar and synthetic aperture radar but also spaceborne passive sensor such as microwave radiometer. Some issues such as protection of 6-7GHz microwave radiometer are still not resolved. <br />Table 1 shows combination of channel to derive geophysical<br /> parameter. In this table, Radio Regulations (R.R. ) was modified in WRC-2000 for 18.6-18.8GHz and in WRC-2007 for 10.6-10.68GHz, 23.6-24GHz and 36-37GHz. Emission is prohibited by R.R.No.5.340 for 10.68-10.7GHz, 23.6-24GHz, 87.5-90.5GHz.<br />3<br />

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1.Introduction (2/2)<br />6-7GHz microwave radiometer is very important and best to observe sea surface temperature and others through clouds.<br />However, this band is not protected in Radio Regulations<br /> (R.R.) of ITU-R. Therefore various interference sources to<br /> 6-7GHz microwave radiometer are classified and introduced.<br />Sharing analysis in land area is conducted [1]. Aircraft<br /> experiment was conducted to measure interference in Japan in 2006 [2]. In the ocean area, there is no analysis to date. <br />In this paper, sharing analysis is shown for the first time in the world.<br />6<br />

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2. INTERFERENCE SOURCES<br />There are the following interference sources to spacebornemicrowave radiometer using 6-7 GHz: <br />(1)Interference from radio ground system <br />There are various interferences in the AMSR-E image as shown in Figures 1 and 2.<br />(2)Scattered emission of down link of feeder link of a mobile satellite over the surface of ocean <br /> There are line-shape interferences in the AMSR-E image as shown in Figure 3. <br />(3) direct radiation from mobile satellite to horn of microwave radiometer via edge of main reflector. <br />There is interference of part of main dish shape in the AMSR-E image as shown in Figure 4. <br />(4)Interference to cold sky mirror for calibration.<br />Calibration accuracy using cold sky mirror is degraded. <br />7<br />

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Radio Regulations No.5.458<br />6-7GHz band is not protected in R.R. No.5.458 which shows that in the band 6 425-7 075 MHz, passive microwave sensor measurements are carried out over the oceans. In the band 7 075-7 250 MHz, passive microwave sensor measurements are carried out. Administrations should bear in mind the needs of the Earth exploration-satellite (passive) and space research (passive) services in their future planning of the bands 6 425-7 025 MHz and 7 075-<br /> 7 250 MHz.<br />Modifications of Radio Regulation may be needed in the future. JAXA is planning to launch AMSR-2 mounted on GCOM-W in November, 2011 which has additional band 7.3GHz (350MHz) to 6.925 GHz (350MHz) band in order to select channel with lower interference.<br />13<br />

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3.2. Interference analysis (2/4)<br />Typical interference in the ocean is caused by scattering at surface of ocean. Interference analysis is conducted by applying radar equations and using Table 2 and 3.<br />Dependence of scattering coefficients on incidence angle are shown in the following figures.<br />20<br />

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23<br />Receiving power Pr of a spaceborne microwave radiometer is given by the following equations:<br />

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3.2. Interference analysis (3/4)<br />Back scattering radar cross section of surface of ocean is obtained in Ref.[5]. This can be converted to forward<br /> scattering as shown in Ref.[6].<br />Forward scattering coefficients is assumed to be a function of a single variable,<br /> the off-specular angle, where off-specular angle is the angle<br /> between the direction of specular reflection and the direction in which the energy is scattered to the receiver of microwave radiometer. <br />24<br />

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3.2. Interference analysis (4/4)<br />In this case, the scattering coefficients is circularly symmetric around the direction of specular angle.<br />When incidence angle at the earth is 55 degree and specular reflection occurs, this is worst case. In this case, Pt is calculated as shown in Table 4. According to Rec.ITU-R RS.1029-2[8], interference level -166dBW (Reference bandwidth 200MHz) should not exceeded for more than 0.1 percentage of sensor viewing area.<br />In the case of specular reflection, it was found that protection level was exceeded by about 33dB for AMSR-E and AMSR2.<br />25<br />

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4. CONCLUSION<br />Various interference sources to a 6-7GHz spaceborne microwave radiometer are classified and introduced. <br />These interferences cause degradation of accuracy of sea surface<br /> temperature, sea surface wind and others. <br />In particular, interferences from scattering of downlink from mobile satellites to gateways at the ocean are analyzed for the first<br /> time in the world. <br />It was found that interference level exceeds protection level by about 33dB in the specular reflection case. Dynamic analysis will be needed to measure interference time percentage. <br />We hope that community of GRSS will make efforts to act to protect 6-7GHz spaceborne microwave band<br />28<br />

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ACKNOWLEDGEMENT<br />The authors would like to thank member of GCOM, JAXA.<br />29<br />